A common stepping motor is structured of predetermined members such as a rotor including a permanent magnet and a rotation shaft, bearings rotatably supporting the rotation shaft of the rotor, coils, inner yokes and outer yokes.
Laser welding is utilized to assemble these members (see, Japanese Patent Laid-Open No. Hei 08-126290). When laser welding is utilized, two members can be joined with each other while being positioned with a high degree of accuracy in comparison with other welding methods.
In the above-mentioned Patent Reference, for example, when a mounting flange is to be joined with an outer yoke, a laser beam is irradiated to penetrate through the mounting flange to locally melt joining faces of the mounting flange and the outer yoke. In this manner, the mounting flange is welded with the outer yoke. Further, similarly, when the outer yoke is to be joined with an inner yoke, the laser beam is irradiated to penetrate through the outer yoke to weld the outer yoke with the inner yoke.
As described above, at the time of laser welding for assembling a motor, laser is irradiated to penetrate at least one or more members to be joined, and joining faces of a plurality of the members are melted and joined with each other.
However, the above-mentioned structure has the following problems. When it is structured that a laser beam is penetrated through a plate-like member such as a mounting flange to be welded, a welded trace is appeared on its surface but the welded part of the plate-like member such as the mounting flange with the outer yoke is not exposed outside. Therefore, the welded state is unable to be directly confirmed visually. In other words, the welded portion between the members do not appear outside and thus the welded state can not be directly confirmed.
Further, a winding coil is provided in the inside of the yokes. Therefore, when the laser beam is irradiated too intense, the laser beam penetrates through the yoke to reach to the winding coil and, as a result, disconnection or short circuit of the winding coil may occur. On the other hand, when the laser beam is too weak, joining strength of the plate-like member with the outer yoke may be insufficient. As described above, adjustment of intensity and time period of the laser beam to be irradiated is required to perform strictly and thus the adjustment is difficult.